The present invention relates generally to the field of oil field production systems and, more particularly, to a method and system for the economical production of oil from otherwise marginal wells.
The present invention is directed to an economical oil lift system and method which reduce initial capital expenditure and operational costs in producing oil from stripper wells. Stripper wells typically produce up to about 10 barrels of oil per day. They may also produce water with the oil in various quantities. Stripper wells of that production volume are marginal economically and can be operated only if the capital and operational costs are reduced.
The present invention provides a method and apparatus for providing those kinds of reduced capital and operational costs. Stripper wells are normally straight and relatively shallow, requiring minimal but necessary installed equipment at significant cost. The typical method of producing a stripper well is to install a wellhead pump jack, a string of sucker rods, and a downhole pump. The wellhead equipment also normally entails a walking beam and electric motor at the surface. All this equipment has a well known cost.
Operational costs include the electricity required to power the pump, and periodic service of the wells. Servicing of a typical stripper well involves periodic removal of the sucker rod string, the tubing string and the downhole pump connected on the end of the sucker rod. Indeed, a workover rig is often required to service shallow wells with pump jack and sucker rods. Workover rigs of necessity involve a larger truck which has to be driven to the remote location of the wellhead, erected over the wellhead and then operated to pull all the tubular goods in the well. That preliminary step, even where the well is only 600 feet deep, takes three or more skilled personnel and requires at least an hour or two of operation ignoring the difficulties of getting the truck to the site and then onto the highway after the service job has been completed. Suffice it to say, the difficulties of servicing can range from relatively easy to tedious and difficult. These are activities and service charges which are avoided by the present oil lift apparatus.
The removal and reinstallation of these servicing components involves a substantial economic outlay. This service routine is typically undertaken to clean out the well when there is an excessive accumulation of sand around the pump or paraffin along the tubing. Sometimes, the sucker rods must be pulled to inspect them and to make appropriate replacements or to install rod guides or scrapers on the sucker rods. Sometimes, sucker rods will drag, thereby damaging the surface of the rod string, and possibly wearing against the adjacent tubular goods.
When all of these costs are taken into account, many wells have too little oil production to justify the expensive of the installation and maintenance of such equipment. Thus, there remains a need for a low cost system and method for production oil from strippers wells. The present invention is directed to such a system and method.
The present invention provides a small, portable oil lift system which may be temporarily installed at a wellhead, operated to produce a quantity of oil, and then moved to another wellhead, or operated as permanent equipment. Such a system eliminates the need to permanently install the expensive pump jack and associated equipment normally used in producing oil from a stripper well. Thus, many of the initial capital expenses for producing oil from a stripper well are significantly reduced.
Service for the present system is also distinctly better. A cased well is normally open from the wellhead down to the bottom of the well. The well in operation with the present invention remains open so that the service personnel can work on the well without the delay of having to pull sucker rods and tubing. Service is done through the wellhead without the preliminary step of installing a workover rig to pull sucker rods.
This disclosure sets out a wellhead system which is installed on a towable rig adjacent to the wellhead which utilizes no tubing or sucker rods. Instead of a sucker rod string operating a downhole reciprocating pump, it employs a drum which spools a lifting cable or wireline. The drum and wireline spooling apparatus and supportive frame are positioned adjacent to the wellhead. This equipment need not be moved at the time of servicing. Rather, the equipment inserted into the well comprises just a bailer and a long wireline. The cable or wireline is relatively small yet has sufficient diameter to support the weight which is carried on it (often, it is called a slick line). The produced oil (and any water which is found with it) is bailed out of the well by an elongate tubular bailer.
The present disclosure sets out an improved bailer where the liquid is removed from the bailer by positive air pressure which displaces the liquid. A 100xe2x80x2 bailer is a preferable length, providing 0.5 barrel of fluid per cycle. With the bailer in excessive of about 30 feet, the liquid head becomes so great that vacuum removal, as disclosed in my U.S. Pat. No. 6,039,544, is not possible.
In the preferred embodiment of the invention, the bailer head is raised to a seal and the a bucket is then pressurized, thereby displacing the retrieved liquid out of the bailer and into a gathering system. When the bailer is in the up position at the top end of its cycle, it delivers the liquid, and is then free to either return down the well for another load of liquid, or be removed from the well so that the system may be transported to another wellhead for further production. Alternatively, the bailer may be left at the well head, and the remainder of the system transported to another wellhead, so that the time involved in setting up and breaking down the retrieval portion of the system is minimized.
For service work, the bailer is simply detached from the wireline, pulled from the wellhead, laid aside for the moment, and easy entry into the well is then obtained. Easy entry reduces the setup time to begin service. If the well is sanded up, it is easy to run a sand bailer or wash tubing into the well to dislodge and retrieve the accumulated sand, etc. At the completion of the service work, the sand removal equipment is simply pulled from the well and the bailer is reinserted into the well. Removal of equipment from the well and restoration of that equipment is done easily.
The present apparatus is summarized as equipment which is located at the surface. That equipment includes an elongate horizontal frame on a portable rig which is either rested on the ground or elevated. The portable rig supports a wireline winding mechanism adjacent to a wireline storage reel or drum. A level wind device is typically included. This provides a slick line which is extended from the storage reel or drum through the level winding device and then over a single measuring pulley. The pulley directs the wireline downwardly into the well borehole or casing. The equipment also includes certain load sensors which respond to the load on the slick line. The load on the line is measured dynamically so that the wireline load alters the motor operation so that the wireline is lowered from the surface, dropped into the liquid accumulated at variable depths in the borehole (casing), filled and then the wireline is retrieved with the filled bailer attached. The filled bailer is pulled to the surface. When the bailer arrives at the surface, a switch is triggered to stop further movement. In conjunction with that operation, the top of the bailer is sealed, and pressurized air then forces or displaces the liquid within the bailer out into an enclosure which encloses the system, before draining into the collection tank.
In addition, this disclosure sets forth an improved bailer construction which is much longer than 30 feet to enable delivery of a greater volume of oil. It is sufficiently long that physics requires removal by air displacement, and not by vacuum lift. A seal is provided which seals the bucket perfectly, thereby enabling air to be pumped into the bailer and force any liquid in the bailer from the bailer into an oil recovery system.
This invention may be operated in several, user-selectable modes. One may choose to operate the system in continuous mode, automatic timed-cycle mode, level control mode, or in manual mode. The system also provides an automatic restart capability, if the system is to be operated without any on-site supervision. In any of these modes, the system saves thousands of dollars per year in electrical cost, manpower, and servicing over previous systems employing a pump jack, sucker rods and pumps. The system offers the additional advantages in that it requires no site preparation, and it is completely mobile so that one unit can produce oil from multiple wells. These and other features and advantages of the invention will be apparent to those skilled in the art.